1. Field of the Invention:
The present invention relates generally to a method of wiring an armature of an electric rotating machine such as a rotor of an electric motor or a rotor of an alternator. More particularly, it relates to such a winding method which is able to reduce an initial unbalance involved in the production of an armature of the electric rotating machine having a plurality of armature windings.
2. Description of the Prior Art:
An armature of a high-speed electric rotating machine such as a rotor of an electric motor or a rotor of an alternator must be balanced about its axis of rotation; if not so, the armature while it is rotating would produce excessive vibration which will cause various serious problems.
In the manufacture of the armature, however, the amount of unbalance involved in the armature generally increases as the assembling of the armature proceeds. This is because amounts of unbalance associated with individual components are accumulated and sometimes enhanced by the assembling method employed. In the case of the rotor for motors or the rotor for alternators, the amount of unbalance involved in the entire windings is considerably large and may exceed 50% of the amount of unbalance of the entire rotor.
In the manufacture of these rotors, a dynamic balancing is used to reduce or cancel out the unbalance created in the course of the manufacture of each rotor. In the case of the rotor for motors, the dynamic balancing is performed by using either a "minus" balancing method in which the outer periphery of an unbalanced rotor is cut on its heavy side, or a "plus" balancing method in which a balancing material such as a so-called patty is attached to a lighter side of the rotor. One example of the plus balancing method is disclosed in Japanese Patent Laid-open Publication No. 62-203535 in which a patty is automatically attached to the light side of a point of unbalance involved in the winding of a rotor.
Correction of unbalancing of an armature of an electric rotating machine needs an additional balancing process using a balancing machine. In case where the patty is used in such balancing process, a tedious and time-consuming adjustment of the amount of patty used is needed. Eventually, the unbalance correction increases the production cost of the armature.
Many armature windings are formed by the lap winding in which the windings are wound around winding portions each composed of one slot formed in the armature. According to the lap winding, the amount of unbalance involved in a first-formed winding wound around a first slot greatly differs from the amount of unbalance involved in a subsequently formed winding wound around a second or succeeding slot. The amount of unbalance is indicated by the product of the mass of a winding and the eccentricity of this winding with respect to the axis of rotation. The difference in the amount of unbalance is created for the reasons described below. The first-formed winding at the first slot is closely fitted with the body of a rotor, while a second-formed winding at the second slot overlaps the first-formed winding. Thus, the length and mass of the second-formed winding are larger than those of the first-formed winding. Since the unbalancing is the product of the mass of the winding and the eccentricity of the winding with respect to the axis of rotation as stated above, a difference in the amount of unbalance is created between the winding formed around the first slot and the winding formed around the subsequent slot. In most cases, the amounts of unbalance created at the second and succeeding slots varies regularly relative to the amount of unbalance created at the first slot. Since the winding formed around the first slot has a smaller amount of unbalance than the windings formed around the second and succeeding slots, the light side of an unbalancing of the entire armature windings is located in the vicinity of the first slot and appears in a substantially constant amount.